1. Field Of the Invention
The invention relates to compatible polymers which demonstrate the phenomenon of "upper critical solution temperature" (UCST), and use of same for registering optically readable information.
2. Discussion of the Background
From Eur. OS 0 177 063, a method is known for recording, storing, and displaying optically readable information in a material medium, wherewith a polyblend P comprised of two disparate but mutually compatible polymers P1 and P2 is employed, said mixture having a lower critical solution temperature (LCST), wherewith an optically differentiable modification of the information storage medium is effected by a phase transformation from a compatible polymer blend (polyblend) below the LCST to de-blended polymers P1 and P2 above the LCST, or by the reverse of this transformation.
There are literature reports of data storage with mixtures of polyvinylidene fluoride and polymethyl methacrylate (PVDF/PMMA) employed as a substrate medium (see 1985 Plastic Industry News, 31 (11)).
In general, it may fairly be stated that the following 1947 statement of Dobry remains valid: "In polyblends miscibility is the exception and immiscibility is the rule." (Dobry, A. and Boyer-Kawenoki, F., 1947, J. Polym. Sci., 1: 90.) However, in the meantime a number of compatible polyblends have been described which are comprised of disparate polymers. (See Olabisi, O., Robeson, L. M., and Shaw, M. T., 1979, "Polymer-polymer miscibility", pub. Academic Press; and 1982 Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 18, 443-478, pub. John Wiley.) The above-recited state of the art also points out means of employing such polyblends with LCST as, e.g., data storage media, and for self-darkening window glazing.
From theoretical considerations (Flory-Theorie, lattice theory), the existence of an LCST and a UCST may be deduced. (See "Kirk-Othmer", loc. cit., pp. 446, 460-547; Olabisi et al., loc. cit.)
The LCST of polyblend systems represents a phenomenon whereby a "cloud point" occurs upon heating; i.e., as temperature is increased a temperature threshold is passed at which the polyblend re-separates into two mutually incompatible polymer phases.
The UCST is characterized by phase separation in a polyblend system at a lower temperature, and development of miscibility (formation of a single phase) at higher temperature.
Recently a number of polymer systems have been discovered which display LCST behavior. In the monograph of Olabisi et al., loc. cit., 267-268, the following is stated:
"This chapter clearly shows that LCST behavior is definitely more common than UCST behavior in polymer blends; therefore increasing the temperature decreases the miscibility."
The UCST phenomenon has been described in a number of publications, e.g., for styrene/butadiene/rubber mixtures (Ougizawa, T., et al., 1985, Macromolecules, 18, 2089); for polystyrene/poly-o-chlorostyrene (Zacharius, S. L., et al., 1984, Adv. Chem. Ser., 206; and 1983, Macromolecules, 16(3):381); for blends of polystyrene and polystyrene/4-bromostyrene copolymer (Strobel, G. R., et al., 1986, Macromolecules, 19(11):2683; and Kambour, R. P., et al., 1986, Marcomolecules, 19(11):2679); for systems comprised of polystyrene and butadiene-methylstyrene copolymer (Kuleznev, V. eN., et al., see CA 102:185811f); for blends of chlorinated polyethylene and PMMA (Walsh, D. J., et al., 1981, Polymer, (22/8):1005); for blends of PVC and PMMA (see Cnalykh, A. E., et al., CA 94:176033t); for blends of high molecular weight chlorinated polyethylenes (Ueda, H., et al., 1985, Macromolecules, 18(12):2719); and for blends of certain methyl-substituted polystyrenes and polystyrene (Sillescu et al., 1986, Macromol. Chem. Rapid Commun., 7:415-419).
Further, UCST behavior is known for blends of polystyrene and carboxylated poly(2,6-dimethyl-1,4phenylene oxide) (see Cong, G., et al., 1986, Macromolecules, 19(11):2765); for blends of polystyrene and poly(vinyl methyl ether) (Kwei, T. K., et al., 1974, Marcomolecules, 7, 667); for blends of PMMA and PVC (Razinskaya, I. N., see CA 104:110546f); for blends of PVC and block copolymers of polybutylene terephthalate and polytetrahydrofuran (Nishi, T., et al., 1975, I. Appl. Phys.,46, 4157); and for blends of disparate acrylonitrile-styrene copolymers (Ougizawa, T., et al., see CA 105:983235).
UCST behavior has also been reported for blends of deuterated and normal polymer species (see Bates, F. S., et al, 1986, Marcomolecules, 19(7):1938; and Yang, H., et al., 1986, Polym. Commun., 27(5):132).
The cited publications are primarily concerned with theoretical aspects of the polymer chemical and physical behavior of these polyblends. The statement of Olabisi et al., from "Polymer-polymer miscibility", loc. cit., p. 322, is applicable: "In terms of property enhancement of specific polymer blends, miscibility per se is not a criterion for utility."
In acrylate chemistry, the basic orientation is that of little prospect of finding compatible polymer blends. Thus, Olabisi et al., loc. cit., pp. 233-238 summarize the known results for poly(meth)acrylates as follows: "The available experience indicates that the various members of the acrylate family are not miscible."
Thus, the prospects of finding polyblends with UCST behavior, and with phase behavior useful for specific industrial or technical purposes, are extremely poor.
However, contrary to the teaching of the literature, acrylate chemistry does in fact include a large number of compatible polyblends, as will be discussed below; and many of these display UCST behavior. Further, it has been discovered that UCST behavior is not confined to polymers of a specific low molecular weight, but may also occur when one of the two polymers is crosslinked.
There is a demand for optical data storage devices, particularly devices which allow erasure of stored data and reuse of the memory capability. The object is to achieve a memory material which memory is maximally insensitive to spurious influences, is uncomplicated in operation, and is inexpensive to manufacture. Further, there is a demand for storage media systems which are reversible, and in particular are reversible at relatively low temperatures. The specific processing conditions should not have a limiting effect on the properties of the memory; i.e., such effects should be minimized.